1. Field of the Invention
The present invention relates to a telescopic suspension fork leg with an inner tube and an outer tube and a damping arrangement and a spring arrangement.
2. Background Art
The telescopic suspension fork leg according to this disclosure can be used, for example, for the formation of a telescopic suspension fork, also abbreviated to “telefork,” which is used on a motorcycle or, for example, on a bicycle. Such a telescopic fork fulfils the function of guiding a front wheel of the vehicle in question, undertakes the task of suspension, and serves for damping when the vehicle moves over uneven areas of the roadway. The telefork provides that the spring movement subsides rapidly again, and also serves to support a braking moment which is built up upon a braking of the front wheel as a reaction moment, relative to the frame of the vehicle.
Owing to the high force demands which are placed on a telescopic fork, a telescopic suspension fork leg which is used for the formation of the telescopic fork possesses a plurality of functionalities and components by which, for example, the spring characteristic and the damping characteristic of the telescopic suspension fork leg can be influenced.
To bring about a damping function for the damping of the oscillating movement of the inner tube and of the outer tube relative to each other, known damping arrangements have bores, through which a damping fluid (for example, a telescopic fork oil) can flow. To achieve a required characteristic in response to the respective specification of the rider or respectively as a reaction to the condition of the roadway surface, the damping arrangement possesses generally adjustable valve arrangements, by which the through-flow behavior of the damping fluid can be adjusted.
When the damping fluid flows through the bores or valves, respectively, very high pressures are formed locally, which are so great that air bubbles develop. This potentially can cause cavitation in some known damping arrangements. In order to prevent cavitation, the damping fluid is placed under high pressure, so that the formation of gas bubbles cannot occur in the first place.
A front wheel fork for a two-wheeled vehicle has become known by means of publication WO 2008/085097 A1. In this known front wheel fork, a telescopic suspension fork leg is provided, which has an inner tube and an outer tube and a damping arrangement and also a spring. The spring is arranged here in a first volume O1, whilst the damping arrangement has a second volume O2, which are sealed hermetically with respect to each other. The damping arrangement of this known type of front wheel fork has two fluid volumes separated from each other, which can be optionally connected with an equalizing reservoir. In this known front wheel fork, the fluid in the first chamber, which holds the spring arrangement, can disadvantageously mix with the fluid in the damping arrangement. For this reason, a third volume is provided, which is preferably filled with air and is intended to prevent a direct contact between the first volume O1 and the second volume O2.
By means of Japanese publication JP 05263826 A, a gas spring has become known, which has a seal which has a greater diameter than a piston rod on which the seal is arranged, supposedly to reduce the friction resistance of the piston rod.
From publication WO 2007/046750 A1 a front wheel fork is known which has a damping arrangement according to the so-called “closed cartridge” principle. This known front wheel fork here has a main spring arranged in the inner tube which is penetrated by a piston rod. On the piston rod, a damper piston is arranged which can carry out a back-and-forth movement in an inner tube of the damper arrangement. In doing so, it displaces a damping fluid present in the damping arrangement out from the interior of the inner tube via apertures which are connected with an annular space arranged coaxially to the interior of the damping tube. The annular space is in turn in fluid communication with a return flow chamber constructed in the inner tube of the damping arrangement, so that both the upper and the lower piston surface of the damping piston are in contact with the damping fluid. With the oscillating movement of the damping piston, the damping fluid is therefore conveyed from the compression chamber into the return flow chamber, wherein as a function of the stroke movement of the damping piston the compression chamber and the return flow chamber interchange.
Such a system operating with parallel damping has the advantage that the damping fluid is constantly under pressure and in this way cavitation is prevented.
In a telescopic suspension fork leg used for the formation of the known front wheel fork, the piston rod extends through a cover of the damping arrangement into the latter, up to the piston, which is fastened to the piston rod. In the known front wheel fork, the air chamber with the main spring is located beneath the damping arrangement. In order to prevent oil from escaping from the damping arrangement in the direction of the air chamber, in the extended state, it is necessary to arrange a sealing arrangement in the region between the piston rod and the cover of the damping arrangement.
In the receiving space of the known front wheel fork, in which the main spring is located, both damping fluid, i.e. oil, and also air are present. On compression of the known front wheel fork, the pressure in the air chamber accommodating the main spring distinctly increases and, via the annular gap between the piston rod and the cover of the damping arrangement, a foamed oil-air mixture penetrates—and hence the effect occurs which is intended to be avoided by a double-acting damping, namely the formation of cavitation.
In addition, the penetration of oil from the air chamber into the damping arrangement leads to an increase of oil volume in the damping arrangement. The result is that the external reservoir, which is provided as an equalization arrangement, comes into solid compression with the piston provided therein for the pre-stressing of the oil volume in the damping arrangement; hence the response behaviour of the known front wheel fork deteriorates substantially, because it hardens and in adds to the risk of damage.
Known from US 2008/0230335 A1 is a front wheel fork which has a damping arrangement that is arranged beneath an upper oil chamber R1 and in which an opening is provided on the piston rod, via which, in the fully compressed state of the front wheel fork, oil can flow out from the damping arrangement under high pressure in the direction of a reservoir R3.
This known front wheel fork therefore has the disadvantage that a fluid flow from the damping arrangement in the direction of a reservoir only takes place in a highly stressed state of the damping arrangement, namely when the front wheel fork is almost completely compressed. Depending on the travel profile covered by the vehicle which is equipped with this known front wheel fork, this state may be rarely or never reached. Also, it is possible that depending on the setting of the response behaviour of the damping arrangement, the state of almost complete contraction of the known front wheel fork is likewise never reached. This leads to an effect with positive feedback, because the oil volume increases in the damping arrangement, the response behaviour of this known front wheel fork becomes noticeably harder for the rider and thereby uncomfortable. This usually leads to a rider then using the vehicle less dynamically, the compression movement of the known front wheel fork thereby decreases, and the damping arrangement fills further with oil and becomes still harder. Precisely the contrary undesired effect therefore is reached, namely a response behavior of the suspension fork which is no longer comparable with the response behaviour to which the rider is accustomed.
The rider of the vehicle is forced to bring about, for example, an emergency braking of the vehicle via the front wheel brake only, in order to achieve such a deep plunging of the front wheel fork that an oil volume equalization can be reached again via the known front wheel fork. It lies within the nature of the matter that this is counterproductive, and is not compatible with the aim of providing the rider of the vehicle with a vehicle having a spring damping behavior which is customary for him and his normal driving habits.
If this known front wheel fork is mounted on a bicycle which is also foreseen for travel over rough terrain, then such a front wheel fork must have large spring travels of up to 300 mm and more, which leads to the fact that an almost complete contraction of the suspension fork, continuing far beyond the normal compression movement, rarely takes place. Accordingly, with a design of the suspension fork according to this known suspension fork described above, a distinct change to the response behavior of the front wheel fork occurs, because it hardens with increasing operation of the vehicle which is equipped therewith—and hence confronts the rider with a response behavior which, for example during a competitive event, distinctly differs from the response behavior at the beginning of the event. This of course is undesirable. If an oil volume equalization then occurs, the response behavior of the known front wheel fork changes yet again, so that the rider is confronted with a non-constant response behavior of the front wheel fork.
By means of US 2010/0207350 A1 a telescopic suspension fork is known, which has a piston rod with a communication passage that allows for an exchange of fluid between the oil chamber in a damper cylinder and an oil chamber outside of the damper cylinder, when the telescopic suspension fork reaches a certain predetermined relieved position (which can be a maximally relieved position). According to one embodiment, the communication passage is a cross-section reduction of the piston rod provided with a constant diameter, as illustrated in FIG. 4 of the US 2010/0207350 A1 patent publication. The cross-section reduction possesses a sharp-edged transition to the non-tapered section. There is, therefore, a discontinuous jump between the tapered and the non-tapered sections. If a piston rod seal provided on the piston rod enters the tapered region due to a spring movement, a fluid exchange between the two oil chambers takes place. If the piston rod seal is located in the non-tapered region, it seals off the two oil chambers from each other. The movement of the piston rod seal across the region of the piston rod harbouring the discontinuous jump leads to a rapid wear of the elastomer piston rod seal. This formation of the cross-section reduction is supposed to serve a simpler manufacturing of the communication passage.
According to an alternative embodiment illustrated in FIG. 5 of US 2010/0207350, a fluid exchange between the oil chambers is possible via two radial communication bores provided in the piston rod. In both cases, the known telescopic suspension fork has a damper cylinder 21 located above, in the area of triple trees, which in a rebounded state of the spring is not located in the oil of the outer chamber, so that uncontrolled oil escape into the outer chamber occurs due to the opening function of the piston rod seal. However, out of the outer chamber air enters into the damper cylinder, which cannot escape to the top, but instead gathers beneath the floating piston. This means that the air cushion beneath the floating mount 61 grows over time and the damping function of the damper cylinder deteriorates.
From the foregoing background, the present invention addresses the problem of providing a telescopic suspension fork leg and a telescopic suspension fork equipped therewith, which reliably brings about an oil volume equalization between the damping arrangement and a reservoir or equalization chamber for damping fluid largely independently of the covered travel profile of the vehicle—and therefore also of possible downtime. A fork equipped therewith hence presents a response behavior which is largely independent of the travel profile.
To solve this problem known in the background art, with regard to the telescopic suspension fork leg, the present invention has fundamental features as indicated herein. Advantageous embodiments hereof are described in the further claims.